1. Field of the Invention
This invention relates to improvements in a fuel vapor treatment canister which is adapted to temporarily store therein fuel vapor generated in a fuel tank and the like and to release the stored fuel vapor at certain timings to be burnt in an engine in order to reduce the amount of fuel vapor emitted from the fuel tank and the like of a vehicle provided with the engine.
2. Description of the Prior Art
Hitherto most automotive vehicles are equipped with a fuel vapor treatment canister including fuel vapor adsorbing material (for example, crushed or granulated activated carbon) stored in a casing. Fuel vapor generated from a fuel tank is adsorbed by the fuel vapor adsorbing material, and then the adsorbed fuel vapor is desorbed from the fuel vapor adsorbing material at certain timings and carried to a combustion device (for example, combustion chambers of an engine, or a combustibles burning device of a vehicle equipped with a fuel cell) under the action of air flowing through the fuel vapor adsorbing material. This prevents fuel vapor from being released into the atmosphere. It will be understood that fuel vapor is generated in the fuel tank, for example, in the following cases:
(a) When an automotive vehicle is allowed to stand, fuel vapor is generated at a high temperature in the daytime under a temperature change between day and night.
(b) When the vehicle is stopped after its cruising (particularly after its high speed cruising), heat of an engine at a high temperature is transmitted to the fuel tank or the like. At this time, the temperature of the fuel tank or the like abruptly rises so that fuel vapor is generated in the fuel tank or the like.
(c) When fuel is supplied into the fuel tank, fuel vapor is generated in the fuel tank.
A typical example of such a conventional fuel vapor treatment canister is disclosed in Japanese Patent Provisional Publication No. 9-112356 and will be discussed with reference to FIG. 13A.
The fuel vapor treatment canister 101 includes a casing 102C. The casing 102C includes a cylindrical casing body 102 which is provided at its one end with a first end wall 103, and at the other end with a second end wall 104. The first end wall 103 has a pipe defining therein a communication opening 103a which is in communication with the atmospheric. The second end wall 104 has an upper pipe defining therein a fuel vapor inlet opening 104a which is in communication with a fuel tank so that fuel vapor is flown in through the opening 104a. The second end wall 104 further has a lower pipe defining therein a fuel vapor outlet opening 104b which is in communication with an air intake passage of an intake system of an internal combustion engine (not shown) so that fuel vapor is flown out through the opening 104b. A perforated dish-like plate 107 is disposed inside the casing body 102 and located adjacent the second end wall 104. The disk-like plate 107 is formed with a plurality of through-holes (not identified) and has a cylindrical flange section (not identified) which is fitted to the inner surface of the casing body 102 and in contact with the second end wall 104 so that a space 106 is defined between the dish-like plate 107 and the second end wall 104. A sheet-like filter 108 formed of a non-woven fabric of polyester or a sheet of polyurethane foam is disposed inside the dish-like plate 107 so as to be in contact with the dish-like plate 107.
A perforated plate 110 is disposed inside the casing body 102 and located adjacent the first end wall 103. Two compression springs 112, 112 are disposed between the perforated plate 110 and the first end wall 103 so as to define a space 109 inside the casing body 102. A filter 111 similar to the filter 108 is disposed inside and in contact with the perforated plate 110. A chamber or inside space Ra between the filter 108 and the filter 111. The chamber Ra is filled with a fuel vapor adsorbing material A1a and a heat-accumulative material A2a which is higher in heat conductivity and specific heat than the fuel vapor-adsorbing material A1a which are in a uniformly mixed state.
In operation, fuel vapor flowing in the canister 101 through the opening 104a is adsorbed by the fuel vapor adsorbing material A1a. At this time, the distribution of concentration of the adsorbed fuel is as shown in FIG. 13B in which the concentration of the fuel vapor is gradually saturated from a side near the second end wall 104 to a side near the first end wall 103. When the adsorption state has reaches a level at which fuel vapor is adsorbed by a portion of the fuel vapor adsorbing material A1a located near the first end wall 103, fuel vapor is released in an amount according to the concentration of the adsorbed fuel vapor at the portion through the opening 103a. It is to be noted that heat is generated so as to raise the temperature of the fuel vapor adsorbing material A1a when fuel vapor is adsorbed by the fuel vapor adsorbing material A1a. A fuel vapor amount corresponding to fuel vapor adsorbing ability of the fuel vapor adsorbing material A1a increases as the temperature rises. However, the heat generated by the fuel vapor adsorbing material A1a is adsorbed by the heat-accumulative material A2a thereby preventing the temperature of the fuel vapor adsorbing material A1a from rising. This prevents the fuel vapor amount corresponding to the fuel vapor adsorbing ability from being lowered.
In the intake stroke of an operational cycle of the engine, vacuum is generated in the air intake passage of the engine and transmitted through the opening 104b into the casing 102C. Accordingly, atmospheric air is introduced through the opening 103a into the casing 102C so as to develop air stream toward the opening 104b. Under the action of this air stream, fuel vapor (hydrocarbons) adsorbed by the fuel vapor adsorbing material A1a is desorbed and sucked through the opening 104b and the air intake passage into the engine to be combusted in the engine.
As shown in FIG. 14A, during desorption of the fuel vapor adsorbed by the fuel vapor adsorbing material A1a after fuel vapor adsorption indicated in FIG. 13B, the concentration of the adsorbed fuel vapor (or a fuel vapor residual level) takes a mode indicated by curves V1 which indicates the case where the fuel vapor adsorbing material A1a and the heat-accumulative material A2a are disposed in the chamber Ra. For reference, a curve V2 indicates a case where only the fuel vapor adsorbing material A1a such as activated carbon is disposed in the chamber Ra.
Additionally, as shown in FIG. 14B, during adsorption of fuel vapor by the fuel vapor adsorbing material A1a after fuel vapor desorption of FIG. 14A, the concentration of the adsorbed fuel vapor takes a mode indicated by a curve V3 which indicates the case where the fuel vapor adsorbing material A1a and the heat-accumulative material A2a are disposed in the chamber Ra. For reference, a curve V4 indicates a case where only the fuel vapor adsorbing material A1a such as activated carbon is disposed in the chamber Ra. FIG. 14B reveals that the fuel vapor residual level (the concentration of the adsorbed fuel vapor) at the respective positions in an axial direction of the canister is low in the case where the fuel vapor adsorbing material A1a and the heat-accumulative material A2a are disposed in the chamber Ra as compared with that in the case where only the fuel vapor adsorbing material A1a is disposed in the chamber Ra. This is because, in case that the fuel vapor adsorbing material A1a and the heat-accumulative material A2a are disposed in the chamber Ra, heat accumulated in the heat-accumulative material A2a is transmitted to the fuel vapor adsorbing material A1a during desorption of fuel vapor from the fuel vapor adsorbing material A1a, so that the temperature of the fuel vapor adsorbing material A1a is prevented from lowering thereby increasing the amount of fuel vapor desorbed from the fuel vapor adsorbing material A1a. 
It will be understood that, in FIG. 14B, the difference between the concentration of adsorbed fuel vapor and the fuel vapor residual level at the side of the first end wall corresponds to the amount of fuel vapor desorbed from the fuel vapor adsorbing material A1a. FIG. 14B also reveals that the amount of fuel vapor adsorbed by the fuel vapor adsorbing material A1a at the respective positions in the flow direction of air and fuel vapor in the chamber R1a is large in the case where the fuel vapor adsorbing material A1a and the heat-accumulative material A2a are disposed in the chamber R as compared with that in the case where only the fuel vapor adsorbing material A1a is disposed in the chamber Ra. As a result, the amount of fuel vapor released from the canister to the atmosphere increases at a time when the amount of fuel vapor adsorbed by the fuel vapor adsorbing material A1a is not so large, in the case where only the fuel vapor adsorbing material A1a is disposed in the chamber Ra as compared with that in case where the fuel vapor adsorbing material A1a and the heat-accumulative material A2a are disposed in the chamber Ra. This is because, in case where only the fuel vapor adsorbing material A1a is disposed in the chamber Ra, the temperature of the fuel vapor adsorbing material A1a increases owing to heat generation at adsorption of fuel vapor to the fuel vapor adsorbing material A1a thereby decreasing the fuel vapor amount corresponding to the fuel vapor adsorbing ability.
As appreciated from the above, it may be advantageous to use the fuel vapor adsorbing material A1a and the heat-accumulative material A2a in the chamber Ra in order that adsorption and desorption of fuel vapor in the canister is required to be quickly accomplished.
However, drawbacks have been encountered in the above conventional fuel vapor treatment canister, as discussed below. For example, when the engine is started and is operated at high speeds upon depression of an accelerator pedal under a condition in which a large amount of fuel vapor has been adsorbed in the fuel vapor adsorbing material in the canister provided with the fuel vapor adsorbing material and the heat-accumulative material in the whole inside space or chamber (Ra) thereof, fuel vapor adsorbed in the fuel vapor adsorbing material is abruptly desorbed from the fuel vapor adsorbing material. At this time, the fuel vapor adsorbing material makes it temperature lowering owing to rapid desorption of fuel vapor from the fuel vapor adsorbing material; however, the temperature lowering can be suppressed upon receiving heat released from the heat-accumulative material. Accordingly, in case that the heat-accumulative material is used mixed with the fuel vapor adsorbing material, the temperature of the fuel vapor adsorbing material can be kept high as compared with a case in which the heat-accumulative material does not exist. As a result, a large amount of fuel vapor is abruptly desorbed so as to increase the fuel vapor construction of intake air to be sucked into the combustion cambers of the engine. This invites disorder of the engine or ineffective combustion within the combustion chambers due to suction of excessive fuel (hydrocarbons) thereby releasing unburned combustion gas (hydrocarbons) into the atmosphere. Japanese Patent Provisional Publication No. 9-112356 discloses also a fuel vapor treatment canister which contains the fuel vapor adsorbing material in the form of a layer and the heat-accumulative material in the form of a layer, in which the two layers are disposed alternate to each other. Such a conventional fuel vapor treatment canister also provides the same disadvantages as those in the above-discussed fuel vapor treatment canister shown in FIG. 13A.
In view of the above, it is an object of the present invention to provide an improved fuel vapor treatment canister which can overcome drawbacks encountered in conventional fuel vapor treatment canisters including ones disclosed in Japanese Patent Provisional Publication No. 9-112356.
Another object of the present invention is to provide an improved fuel vapor treatment canister which can effectively prevent an engine from becoming disordered and unburned hydrocarbons from being emitted to the atmosphere while increasing its fuel vapor adsorbing ability, thereby totally reducing emission of hydrocarbons to the atmosphere.
A further object of the present invention is to provide an improved fuel vapor treatment canister which can effectively prevent a large amount of fuel vapor from being abruptly sucked into an engine while increasing the amount of a fuel vapor adsorbing material disposed in the canister without enlarging the size of the canister.
A still further object of the present invention is to provide an improved fuel vapor treatment canister having a fuel vapor adsorption chamber and a heat accumulation and fuel vapor adsorption chamber, which is adapted to prevent heat generated in the fuel vapor adsorption chamber from being transmitted to the heat accumulation and fuel vapor adsorption chamber thereby preventing lowering in fuel vapor retaining ability of the fuel vapor adsorbing material in the heat accumulation and fuel vapor adsorption chamber which lowering it owing to temperature rise of the fuel vapor adsorbing material in the heat accumulation and fuel vapor adsorption chamber.
An aspect of the present invention resides in a fuel vapor treatment canister comprising a casing arrangement having first and second end walls between which first and second chambers are formed. The first end wall has a portion defining a first opening in communication with a fuel tank, and a portion defining a second opening in communication with an air intake passage of an engine. The second end wall has a portion defining a third opening in communication with atmosphere. The first chamber is located closer to the first end wall than the second chamber. A first fuel vapor adsorbing material is disposed in the first chamber, while a second fuel vapor adsorbing material and a heat-accumulative material are disposed in the second chamber. The heat-accumulative material is larger in specific heat than the second fuel vapor adsorbing material.
A second aspect of the present invention resides in a fuel vapor treatment canister comprising a casing having first and second end walls between which an inside space is formed. The first end wall has a portion defining a first opening in communication with a fuel tank, and a portion defining a second opening in communication with an air intake passage of an engine. The second end wall has a portion defining a third opening in communication with atmosphere. The inside space includes first and second chambers. The first chamber is located closer to the first end wall than the second chamber. A first fuel vapor adsorbing material is disposed in the first chamber, while a second fuel vapor adsorbing material and a heat-accumulative material are disposed in the second chamber. The heat-accumulative material is larger in specific heat than the second fuel vapor adsorbing material.
A third aspect of the present invention resides in a fuel vapor treatment canister comprising a casing having first and second end walls between which an inside space is formed. The first end wall has a portion defining a first opening in communication with a fuel tank, and a portion defining a second opening in communication with an air intake passage of an engine. The second end wall has a portion defining a third opening in communication with atmosphere. The inside space includes first and second chambers. The first chamber is located closer to the first end wall than the second chamber. A partition wall structure is disposed to divide the inside space into the first and second chambers. The partition wall structure has an air permeability and a heat insulating ability higher than that of metal. A first fuel vapor adsorbing material is disposed in the first chamber. A second fuel vapor adsorbing material and a heat-accumulative material are disposed in the second chamber. The heat-conductive material is larger in specific heat than the second fuel vapor adsorbing material.
A fourth aspect of the present invention resides in a fuel vapor treatment canister comprising a first casing having first and second end walls between which a first chamber is formed. The first end wall has a portion defining a first opening in communication with a fuel tank, and a portion defining a second opening. Additionally, a second casing is provided having third and fourth end walls between which a second chamber is formed. The third end wall has a portion defining a third opening in communication with the second opening of the first casing. The fourth end wall has a portion defining a fourth opening in communication with atmosphere. A first fuel vapor adsorbing material is disposed in the first chamber, while a second fuel vapor adsorbing material and a heat-accumulative material are disposed in the second chamber. The heat-accumulative material is larger in specific heat than the second fuel vapor adsorbing material.